update travis: using clang as workaround the c++11 issue
update travis: using clang as workaround the c++11 issue

grame-cncm/libmusicxml,grame-cncm/libmusicxml,arshiacont/libmusicxml,dfober/libmusicxml,arshiacont/libmusicxml,dfober/libmusicxml,grame-cncm/libmusicxml,grame-cncm/libmusicxml,dfober/libmusicxml,arshiacont/libmusicxml,grame-cncm/libmusicxml,grame-cncm/libmusicxml,arshiacont/libmusicxml,dfober/libmusicxml,arshiacont/libmusicxml